My rewind crank fell off but I still have it and trying to figure how to get it back on. In the meanwhile, the rewind wheel still works.

If the rewind "cap" loosens on the rewind shaft, tension goes off the spring that holds the rewind crank in place in the "cap". Put a strip of wood (or something) through the slot in the inner end of the rewind shaft to loosen/tighten the shaft in the "cap".